Implantable medical devices such as pacemakers, defibrillators, and implantable cardioverter defibrillators (“ICDs”) have been successfully implanted in patients for years for treatment of heart rhythm conditions. Pacemakers are implanted to detect periods of bradycardia and deliver low energy electrical stimuli to increase the heart rate. ICDs are implanted in patients to cardiovert or defibrillate the heart by delivering high energy electrical stimuli to slow or reset the heart rate in the event a ventricular tachycardia (VT) or ventricular fibrillation (VF) is detected. Another type of implantable device detects an atrial fibrillation (AF) episode and delivers electrical stimuli to the atria to restore electrical coordination between the upper and lower chambers of the heart. Still another type of implantable device stores and delivers drug ad/or gene therapies to treat a variety of conditions, including cardiac arrhythmias. The current generation for all of these implantable devices are typically can-shaped devices implanted under the skin that deliver therapy via leads that are implanted in the heart via the patient's vascular system.
Next generation implantable medical devices may take the form of elongated intravascular devices that are implanted within the patient's vascular system, instead of under the skin. Examples of these intravascular implantable devices are described, for example, in U.S. Pat. No. 7,082,336, U.S. Published Patent Application Nos. 2005/0043765 A1, 2005/0208471A1 and 2006/0217779A1. These devices contain electric circuitry and/or electronic components that are hermetically sealed to prevent damage to the electronic components and the release of contaminants into the bloodstream. Due to the length of these implantable devices, which in some cases can be approximately 10-60 cm in length, the devices generally are designed to be flexible enough to move through the vasculature while being sufficiently rigid to protect the internal components.
The issue of how to secure such an implantable device in the vasculature is one of the challenges for this next generation of intravascular implantable devices. In addition to the mechanical and operational considerations related to an anchoring system, there are physical and biological implications for the patient, as well as considerations for how an anchoring system may affect the manner in which the implantable device delivers therapy.
As described in some of the embodiments shown in U.S. Pat. No. 7,082,336 and U.S. Published Patent Application No. 2004/0249431, the anchoring system was arranged proximate the middle of the intravascular implantable device so as to be positioned in the vena cava within the thorax. This arrangement anchored the intravascular implantable device near the middle of the patient's torso at a location generally corresponding to the diaphragm. In some embodiments, the anchoring system was integrated with the body of the intravascular implantable device. In other embodiments, the anchoring system was a separate device, such as a stent, that was used to pin the body of the intravascular implantable device in position between the stent and the vessel wall. In still other embodiments, a lead extending from a distal end of the body of the intravascular device would also be anchored in the vasculature, such as in a subclavian vein.
An alternative integrated anchoring system for an intravascular implantable device is described in some of the embodiments shown in U.S. Published Patent Application No. 2005/0208471A1. This alternative integrated anchoring system utilized a radially expandable member positioned proximate the middle of the body of the device to secure the device. In some embodiments, the radially expandable member centered the device within the diameter of the vessel. In other embodiments, two or more radially expandable members were used to secure the middle of the body of the device within a vessel.
The approaches of securing an intravascular implantable device within the thorax by an anchoring system proximate the middle of the body of the device and positioned in the vena cava generally corresponding to the diaphragm of the patient were intended to create a secure and balanced anchoring of the device within the largest diameter vessel in the body. These approaches sought to reduce issues of thrombosis and potential dislodgement of the anchoring system due to impact or movement of the patient.
While intravascular implantable devices represent a significant improvement over conventional implantable devices that are implanted subcutaneously, there are opportunities to improve and refine the designs for such intravascular devices. Accordingly, it would be desirable to provide for an improved design of an anchoring arrangement for an intravascular implantable device.